Kinetics and mechanism of chromium(III)-catalysed oxidation of ethane-1,2-diol and propane-1,2-diol by cerium(IV) in aqueous sulfuric acid media

The kinetics and mechanism of chromium(III)-catalysed oxidation of the title diols by cerium(lv) in aqueous sulfuric acid media to their corresponding aldehydes through the C-C bond cleavage (i.e. glycol splitting) under the conditions, [diol]T much greater than [Ce-IV]T much greater than [Cr]T at different temperatures (35-50 degrees) have been studied. In 1.0 mol dm(-3) sulfuric acid media, the experimentally observed rate law conforms to -d In [Ce-IV]dt = k(obs) = a[diol]T[Cr]T/{b + c[Cr]T} where, [diol]T and [Cr]T give the total concentrations of the substrate and catalyst, respectively; a, b and c are constants at a particular temperature and fixed [H2SO4]. The process has been found acid-catalysed. From the hydrogen sulfate dependence, Ce(SO4)(2) has been identified as the kinetically active species. The proposed mechanism involves the formation of an intermediate involving: the oxidant, catalyst and substrate, and a Cr-III/Cr-IV catalytic cycle has been suggested to operate.